High-frequency electron discharge device of the traveling wave type



Dec. 11, I951 N, UNDENBLAD 2,578,434

HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPEFiled June 25, 1947 3 Sheets-Sheet 1 Rf. INPUT INVENTOR.

nus E. LINDENBLAD ATTORNEY Dec. 1-1, 1951 N. E. LINDENBLAD 2, 8,

HIGHJREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPE FiledJune 25, 1947 3 Sheets-Sheet 2 .//3- soomg MPER MPER Ol-ORDER 0F 0mml00-l250llM$ 100-125 OIIMS 1004250 1415 55mm Ill/IVDRFD INVENTOR.

o/ms NILS E. LINDENBLAD 1951 N E LINDENBLAD 2,573,434

H'IGHFREQUEN CY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPEFiled June 25, 1947 3 Sheets-Sheet 3 m: m/pur ;9- MAGNET/L m5 FIELD COILR. F. M/Pl/T LIA/E /8 l l l Rf. UI/TPUT ZINE INVENTOR.

NILS E LINDENBLAD BY [W83 I ATTORNEY Patented Dec. 11, 1951HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPE NilsE. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application June 25, 1947, Serial No.756,851

17 Claims. 1

This invention relates to improvements in electron discharge devices ofthe growing wave type, especially adapted for use at ultra and very highfrequencies.

An object of the invention is to provide an improved electron dischargedevice capable of amplifying a wide band of high frequencies and whichdoes not depend upon resonance phenomenon in the output circuit.

Another object is to provide a growing wave (sometimes called atraveling wave) type tube having an outer metallic shell or envelopesur' rounding a helical or spiral line, and Which is of such geometricconfiguration as to gradually change the characteristic impedance of thehelical line from a relatively high value in the center of the line to alower value near the ends of the line.

A further object is to enable the terminals of a helical conductor in agrowing Wave type tube to match the characteristic impedance ofconnecting coaxial transmission lines.

A still further object is to provide a wide band helical line type ofgrowing wave amplifier tube for use at high frequencies, which preventsor minimizes the occurrence of parasitics at very high frequenciesoutside the range of frequencies to be amplified.

A detailed description of the invention follows in conjunction with thedrawings, wherein:

Figs. 1, 3 and 4 show three diflerent embodiments of the invention, and

Figs. 2a to 2 inclusive show six different types of coupling orimpedance transformation circuits which can be used between theterminals of the amplifier tube of the invention and the connectingcoaxial transmission lines.

Referring to Fig. 1 in more detaiLthere is shown a wide band growingwave amplifier tube of the broad general type described in my U. S.Patent No. 2,300,052, granted October 27, 1942, and in my copendingapplication Serial No. 724,330, filed January 25, 1947, in which ahelical conductor surrounds a stream of electrons and i in energycoupling relation thereto. The improved amplifier tube of Fig. 1.comprises a tubular non-magnetic metallic envelope or shell it! whichsurrounds a helical conductor II. A suitable cathode is provided at oneend of the tube for furnishing a concentrated heavy stream of electronswhich pass through the interior of the helical conductor I I and whichis finally collected by a. collector electrode 2. at the other end. ofthe tube; This cathode is. shown, by way of example. as comprising acylinder I4 which has only a portion l5 thereof sprayed with electronemitting material. A repeller electrode It at the cathode end of thetube serves to repel or concentrate the electrons emitted by the cathodetoward the helical conductor II. A magnetic field coil I'I surrounds thetube and is energized by a direct current source I8 in series with avariable resistor I9. The field coil is so arranged that the lines offiux extend parallel to the tube in an axial direction in order to focusthe beam of electrons along the center of the tube. It should be notedthat the repeller electrode it is maintained at a negative potentialrelative to the cathode, while the collector electrode I2 is maintainedat a slight positive potential relative to the cathode. In theconstruction of the tube, it may be desirable for the collectorelectrode t be at a slight negative potential relative to the cathode oreven at the same potential as the cathode. The metallic envelope iii isat ground potential which is equivalent to a positive potential withrespect to the cathode. A coaxial transmission line I3 supplies radifrequency input current to one terminal of the helical conductor II,while the amplified current is abstracted from the other terminal of thehelical conductor I I by an output coaxial line 20.

In order to assure a vacuum tight shell or envelope Ill, glass beads 21are provided in the input and output coaxial lines at a locationnearshell Ill. Obviously, the glass beads can be positioned at anysuitable location.

The helical conductor I I is a plurality of wavelengths longperipherally along the helix at the center frequency of operation. Theinput energy supplied to the helix II by input line I3 causes theelectrons passing through the interior of the helix iI to be bunched.The helix II has such dimensions as to couple properly with the electronstream passing along the axis.

The characteristic impedance of this helical conductor is of the orderof several hundred ohms, whereas the characteristic impedances of thecoaxial lines I3 and 2c are each of the order of 50 ohms, as an example.In order to match the impedances of the coaxial lines I3 and 29 to thecharacteristic impedance of the helical conductor I I, to prevent theproduction of standing waves due to reflections at the junction betweenthe lines it and 20 and the conductor Ii, the metallic envelope it istapered in diameter toward its ends so as to reduce the characteristicimpedance of the helical conductor I I gradually oaxial lines to whichit is connected. In order to taper the impedance of the helicalconductor I I down to approximately 50 ohms, which is assumed to be theimpedance of the coaxial lines, the distance between the last turn ofthe coil II and the siurounding tapering shell I should be of the orderof the radius of the wire constituting the coil II. Because this mightbe difiicult to achieve in practical conditions due to the very closespacing required, it will sometimes be more convenient not to taper thecharacteristic impedance of the helical conductor II down as far as 50ohms, but rather to a value of the order of 100 to 125 ohms, in whichcase the spacing between the last turn of the coil II and the taperingenvelope I8 can be larger. In this last case, it is advisable andpreferred that a transmission line link having tapering impedance beinserted externally of the tube between the last turn of the coil I Iand the 50 ohm coaxial line.

Figs. 2d, 2e and 2f show three difierent arrangements for connecting atransmission line link having tapering impedance between the last turnof the coil I! and a 50 ohms coaxial transmission line shown as I3 inFigs. 203, 2c and 21. In Fig. 2d the transmission line link or impedancetransformer, so to state, is labeled 25 and has an inner conductor ofgradually increasing diameter. It should be noted that the length of thetransmission line 25 is of the order of two wavelengths at the meanoperating frequency. The inner conductor of the link 25 is relativelysmall at the end connected directly to the coil II and increases indiameter to a maximum at the end connected to the coaxial line I3. Thegradual change in diametric ratio between the inner and outer conductorsof the link 25 elfects the impedance transformation. Fig. 2c shows anarrangement equivalent to that of Fig. 2d, the difference being thatthis link identified as 25' has the outer conductor changing in diameterrather than the inner conductor. In Fig. 2f the transmission line linkis identified as 25" and has an inner conductor which is coiled and hascloser spacing between turns thereof near the helical conductor II thannear the coaxial line I3. The

. radius of the spiral may also be made smaller as the pitch increases.The outer conductor diameter may also taper down in this direction. Thethree arrangements of Figs. 2d, 2e, and 2 are equivalent to each otherand show an impedance transformation means for coupling the lowimpedance coaxial line I3 to the higher impedance terminal of thehelical conductor II.

It should be understood that the arrangements of Figs. 2d, 2e and 2 maybe used at both terminals of the helical conductor II, when thecharacteristic impedance of the helical conductor is not lowered to apoint where it exactly matches that of the coaxial line to which it isconnected. The arrangements of Fig. 1 as shown, or in combination withcoupling circuits of Fig. 2d, 26 and 2f insure substantially perfectimpedance matching between the helical conductor I I and the input andoutput lines for all frequencies which can be amplified by the growingwave tube. The helical coil I I is designed to have as low attenuationas practical without enabling undesired refiections along the coil I Ito produce parasitics.

Figs. 2a, 2b and 20 show arrangements which can be connected to theinput and output radio frequency carrying lines for assuring suitableground return. In Fig. 2a the coaxial line is shown connected to afolded dipole 30. Fig. 2b shows the coaxial line connected to a suitablewave guide 3| for receiving input waves from iii 4 the wave guide orsupplying amplified output waves to the wave guide. Fig. 2c shows aquarter Wave stub 32 connected between the terminal of the helicalconductor II and a sleeve type antenna 33.

In the arrangements of Figs. 2a to 21 inclusive only those portions ofthe growing wave amplifier tube of the invention have been shown whichare necessary for an understanding of the principles involved. Thus, inthese figures the conical tapering end of the metallic shell has beenshown and only a few turns of the helical con ductor II near one of itsterminals. It will be understood that the remaining portion of thegrowing wave amplifier tube not shown in these figures may take the formshown in Fig. 1, or those of Figs. 3 and 4 described hereinafter.

In constructing the growing wave vacuum tube in accordance with theinvention, it is advanc tageous to provide a coil II which has no lossat the frequencies to be amplified, so that as much as possible of thekinetic energy of the bunched electrons can be transferred to theworking load. At other frequencies, it is of course irnmaterial whethera loss occurs internally or ex ternally of the tube. The arrangement,however, should be such that sufiicient loss is introduced to preventparasitic oscillations, and one way that this can be done is byemploying external trap circuits or deflecting circuits which willconnect artificial loads (damping circuits) to the tube.

Fig. 3 shows an arrangement employing the principles of the invention,wherein parasitics can be prevented at very high frequencies out--' sidethe range to be amplified at which the conducting metallic shell IU mayprovide undesired. cavity resonance conditions. This is done byemploying reactive impedance elements in the form of absorber resistors5s connected to ca-' pacity pick-up plates 5|. These pick up' plates- 5]are uniformly distributed along at least a substantial portion of thelength of the helical conductor II and have such dimensions that theirreactance is very high in the operating frequency range but becomes lowat frequencies higher than the highest operating frequencies. At thesefrequencies higher than the operating frequency, the low reactancebetween the helical conductor I I and the capacity pick-up plates will.permit sumcient current to pass into the resis tors 50 to introduce thedesired damping effect to prevent the production of standing waves onthe conductor II.

The tube, with reactive impedance elements distributed along the helicalconductor, as shown in Fig.3, is claimed in my divisional applica' tionSerial No. 229,072, filed May 31, 1951.

Fig. 4 shows another embodiment of the in-' tor II is connected to theinput coaxial line.

I3, while the other end is terminated by a resistor I0 whose valuematches the characteris tic impedance of the helix II at that end. Asuitable metallic partition having an aperture BI therein serves toseparate the twochan bers. cathode 81! provided with a repellerelectrode III,

The output chamber includes a second.

ductor along the axis of said tube, means for projecting a stream ofelectrons coaxially with respect to said helical conductor, a hollowcylindrical non-magnetic metallic element also positioned coaxially withrespect to said helical conductor and spaced therefrom and extendingover substantially the entire length of said helical conductor, thespacing between said cylindrical metallic element and said helicalconductor decreasing from a point intermediate the ends of said helicalconductor toward one terminal of said helical conductor, whereby thecharacteristic impedance of said helical conductor changes over thatportion of the length thereof measured from said intermediate pointtoward said one terminal, and a line adapted to carry radio frequencycurrents coupled to said one terminal.

7. An electron discharge device comprising a helical conductor, meansfor projecting a stream of electrons through the interior of saidhelical conductor, a metallic shell surrounding said helical conductorover substantially the entire length thereof and spaced therefrom, thespacing between said shell and said helical conductor increasing fromboth ends of said helical conductor toward spaced points intermediatethe ends of said helical conductor, the diameter of said shell beinguniform between said spaced points, means for producing a magnetic fieldhaving fiux lines running parallel to the axis of said helicalconductor, and coaxial transmission lines having characteristicimpedances different from that of said helical conductor coupled to-bothends of said helical conductor.

8. An electron discharge device as defined in claim 7, wherein saidshell is the outer envelope of said device, and means are provided forsealing said envelope at the locations where said transmission linesjoin with said envelope.

9. An electron discharge device comprising first and second chambersplaced longitudinally end-to-end, the side walls of said chambers beingconstituted by a continuous cylindrical inetallic tube, means forprojecting a stream of electrons from one chamber into and through theother chamber, a helical conductor in each of chambers in energytransfer relation to said stream, the side walls of each chamber beingspaced from the helical conductor contained therein, the spacing betweenthe side walls of each chamber and the enclosed helical conductor beingnon-uniform and increasing from one terminal of the helical conductortoward a point intermediate the ends of said helical conductor, and aradio frequency carrying medium coupled to said one terminal. Y

10. An electron discharge device comprising first and second chambersplaced longitudinally end-to end, the side walls of said chambers beingconstituted by a continuous cylindrical metallic tube, means forprojecting a stream of electrons from one chamber into and through theother chamber, a helical conductor in each-of said chambers in energytransfer relation to said stream, the side walls of each chamber beingspaced from the helical conductor contained therein, the spacing betweenthe side Walls of each chamber and the enclosed helical conductor beingnon-uniform and increasing from one terminal of the helical conductortoward a point intermediate the ends of said helical conductor, a radiofrequency input coaxialline coupled to said one terminal of one helicalconductor, and a radio frequency output coaxial-line coupled to said oneterminal of the other helical conductor.

11. An electron discharge device comprising first and second chambersplaced longitudinally end-to-end, an apertured partition between saidchambers for enabling electrons to pass therethrough, a cathode nearthat end of said first chamber farthest removed from said partition, anda cathode in said second chamber at a location near said partition andshielded by said partition from said first cathode, whereby theelectrons emanating from the cathode in said second chamber add to theelectrons emanating from said first cathode and passing through saidpartition.

12. An electron discharge device comprising first and second chambersplaced longitudinally end-to-end, an apertured partition between saidchambers for enabling electrons to pass therethrough, a cathode nearthat end of said first chamber farthest removed from said partition, anda cathode in said second chamber at a location near said partition,whereby the electrons emanating from the cathode in said second chamberadd to the electrons emanating from said first cathode and passingthrough said partition, means for focusing the electrons from saidcathodes into a stream passing in one general direction, and a helicalconductor in each of said chambers positioned to be in energy couplingrelation to said stream.

13. An electron discharge device comprising first and second chambersplaced longitudinally end-to-end, the side walls of said chambers beingconstituted by a continuous cylindrical metallic tube, a helicalconductor in each of said chambers positioned around the axis thereof,said chambers being separated by an apertured partition for enablingelectrons to pass therethrough, a cathode in said first chamber arrangedto pass a concentrated stream of electrons through the interior of thehelical conductor in said first chamber and through the aperturedpartition, and a cathode in said second chamber located near saidpartition for producing additional electrons which add to the electronsfrom said first chamber for passing through the interior of the helicalconductor in said second chamber, said helical conductors being inenergy transfer relation to said electron stream, an input circuitcoupled to the helical conductor in said first chamber, and an outputcircuit coupled to the helical conductor in said second chamber.

14. An electron discharge device as defined in claim 9, wherein saidmeans for projecting a stream of electrons includes a cathode in each ofsaid chambers.

15. An electron discharge device adapted to operate over a predeterminedfrequency range comprising a helical conductor, means for projecting astream of electrons through the interior of said helical conductor, saidhelical conductor being positioned to be in energy coupling relation tosaid stream, a metallic shell surrounding said helical conductor andspaced therefrom, a transmission line having a characteristic impedancedifferent from that of said helical conductor and coupled to saidhelical conductor, the spacing between said shell and helical conductorgradually decreasing from a point intermediate the ends of said helicalconductor to the junction point of said line and helical conductor, aplurality of spaced capacity pick-up elements spaced from said helicalconductor and connected to said shell through absorber elements, there-- actance values of said pick-up elements being relatively high insaid operating range of said discharge device and relatively low atfrequencies higher than the highest operating frequency of said range.

16. An electric tube comprising a helical conductor effectively dividedinto two parts, means for projecting a stream of electrons coaxiallywith respect to said helical conductor and over substantially the entirelength thereof, a hollow metallic shell surrounding said helicalconductor and spaced therefrom, the diameter of said shell increasingfrom opposite ends of said helical conductor to spaced pointsintermediate said opposite ends, the diameter of said shell between saidpoints being uniform, an input circuit coupled to one end of saidhelical conductor and an output circuit coupled to the opposite end ofsaid helical conductor.

17. An electron discharge device comprising first and second chambersplaced longitudinally end-to-end, an apertured partition between saidchambers for enabling electrons to pass therethrough, a cathode nearthat end of said first chamber farthest removed from said partition, andacathode in said second chamber at a loca- 10 tion near said partitionand shielded by said partition from said first cathode, whereby theelectrons emanating from the cathode in said second chamber add to theelectrons emanating from said first chamber and passing through saidpartition, means for focusing the electrons from said cathodes into astream passing in one general direction, and a helical conductor in eachof said chambers positioned to be in energy coupling relation to saidstream.

NILS E. LINDENBLAD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 21,739 Llewellyn Mar. 4, 19412,103,507 Zworykin Dec. 28, 1937 2,233,126 Haeff Feb, 25, 1941 2,289,756Clavier et a1. July 14, 1942 2,300,052 Lindenblad Oct. 27, 19422,367,295 Llewellyln Jan. 16, 1945 2,409,913 Tonks Oct. 22, 1946

